The present invention relates to a system for retaining data on a data rewritable or write-once large capacity recording medium such as a magneto-optic disk (MO) and an optical disk or a magnetic disk etc.
Large capacity recording mediums, having several hundred mega bytes have been highlighted with paperless information in hospitals and government offices.
Among those mediums, large capacity magneto-optic disk and write-once CD-R (Compact-Disk Recordable) have gained a bright prospect because of their high propagation to the public and easy availability.
The MO is, however, easy to erase and add the data, and hence an illegal act such as rearranging, replacing or deleting the data recorded on the MO (which are termed "falsification"), or falsifying the date data on a document file can easily be conducted.
On the other hand, with respect to the CD-R capable of only the write-once operation, it happens that only the medium recorded with inconvenient data is disposed of, and it is impossible to prevent such an act that the data on the CD-R are, after temporarily reading to a computer, falsified, and the falsified data are written to other CD-R.
For preventing the respective illegal acts described above, there has been contrived a system of warranting a validity of the data, which involves executing a signatory process of the data recorded on the medium by use of a hash function, encrypting the statically processed data with a public key supplied from an authentication center, recording the encrypted result as a check sum (CS) in an area different from the data area on the same medium, and decrypting the check sum (CS) by use of a secret key corresponding to the public key.
This system is, however, although the falsification of the data on the same medium can be prevented to some extent, incapable of preventing the falsification of the date data, the disposal of the inconvenient medium, and the write of the falsified data to other medium and is not therefore suited to recording the data of official documents etc obliged to preserve for fixed years as official records and requiring the warrant of the validity thereof.
It is a primary object of the present invention, which was contrived in view of such problems, to provide a data retaining/managing system capable of warranting a validity of data recorded on a medium.